On Upper Tropospheric Kinematics and Severe Weather Occurrence

McNulty, Richard P.

doi:10.1175/1520-0493(1978)106<0662:outkas>2.0.co;2

Cited by 38 publications

(16 citation statements)

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“…The goals of this article are to 1) trace the historical usage of MFC as a forecast tool to understand the physical rationale behind its origin, 2) investigate horizontal mass convergence as a more appropriate diagnostic in an ingredients-based methodology (e.g., McNulty 1978a;Doswell 1987;Johns and Doswell 1992) for forecasting CI, and 3) raise awareness of elevated convection. In section 2 of this article, we review the physical expression of MFC.…”

Section: Introductionmentioning

confidence: 99%

The Use of Moisture Flux Convergence in Forecasting Convective Initiation: Historical and Operational Perspectives

Banacos¹,

Schultz

2005

Weather and Forecasting

257

171

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Moisture flux convergence (MFC) is a term in the conservation of water vapor equation and was first calculated in the 1950s and 1960s as a vertically integrated quantity to predict rainfall associated with synoptic-scale systems. Vertically integrated MFC was also incorporated into the Kuo cumulus parameterization scheme for the Tropics. MFC was eventually suggested for use in forecasting convective initiation in the midlatitudes in 1970, but practical MFC usage quickly evolved to include only surface data, owing to the higher spatial and temporal resolution of surface observations. Since then, surface MFC has been widely applied as a short-term (0-3 h) prognostic quantity for forecasting convective initiation, with an emphasis on determining the favorable spatial location(s) for such development.A scale analysis shows that surface MFC is directly proportional to the horizontal mass convergence field, allowing MFC to be highly effective in highlighting mesoscale boundaries between different air masses near the earth's surface that can be resolved by surface data and appropriate grid spacing in gridded analyses and numerical models. However, the effectiveness of boundaries in generating deep moist convection is influenced by many factors, including the depth of the vertical circulation along the boundary and the presence of convective available potential energy (CAPE) and convective inhibition (CIN) near the boundary. Moreover, lower-and upper-tropospheric jets, frontogenesis, and other forcing mechanisms may produce horizontal mass convergence above the surface, providing the necessary lift to bring elevated parcels to their level of free convection without connection to the boundary layer. Case examples elucidate these points as a context for applying horizontal mass convergence for convective initiation. Because horizontal mass convergence is a more appropriate diagnostic in an ingredients-based methodology for forecasting convective initiation, its use is recommended over MFC.

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Section: Introductionmentioning

confidence: 99%

The Use of Moisture Flux Convergence in Forecasting Convective Initiation: Historical and Operational Perspectives

Banacos¹,

Schultz

2005

Weather and Forecasting

257

171

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“…This unstable air likely served as the inflow to the bands after having risen aloft above the frontal zone. Thus, this event had the three ingredients for deep, moist convection: lift, moisture, and instability (e.g., McNulty 1978;Johns and Doswell 1992). Lift was provided by lower-tropospheric frontogenesis in a synoptic situation rather unimpressive for quasigeostrophic ascent (e.g., straight zonal flow).…”

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confidence: 99%

Banded Convection Caused by Frontogenesis in a Conditionally, Symmetrically, and Inertially Unstable Environment

Schultz

Knox

2007

Monthly Weather Review

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Several east-west-oriented bands of clouds and light rain formed on 20 July 2005 over eastern Montana and the Dakotas. The cloud bands were spaced about 150 km apart, and the most intense band was about 20 km wide and 300 km long, featuring areas of maximum radar reflectivity factor of about 50 dBZ. The cloud bands formed poleward of an area of lower-tropospheric frontogenesis, where air of modest convective available potential energy was being lifted. During initiation and maintenance of the bands, mesoscale regions of dry symmetric and inertial instability were present in the region of the bands, suggesting a possible mechanism for the banding. Interpretation of the extant instabilities in the region of the bands was sensitive to the methodology to assess the instability. The release of these instabilities produced circulations with enough vertical motion to lift parcels to their lifting condensation level, resulting in the observed cloud bands. A high-resolution, numerical weather prediction model demonstrated that forecasting these types of events in such real-time models is possible, although the timing, evolution, and spacing of the bands were not faithfully reproduced. This case is compared to two previous cases in the literature where banded convection was associated with a combination of conditional, symmetric, and inertial instability.

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“…The three ingredients required for convection initiation are moisture, instability, and a lifting mechanism (McNulty 1978;Doswell 1987;Johns and Doswell 1992). The relative humidity between the surface and 500 hPa was computed using sounding relative humidity data weighted by the depth of each measurement.…”

Section: B Convection Initiationmentioning

confidence: 99%

A Case Study on the Impact of Moisture Variability on Convection Initiation Using Radar Refractivity Retrievals

Bodine

Heinselman

Cheong

et al. 2010

Journal of Applied Meteorology and Climatology

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A case study illustrating the impact of moisture variability on convection initiation in a synoptically active environment without strong moisture gradients is presented. The preconvective environment on 30 April 2007 nearly satisfied the three conditions for convection initiation: moisture, instability, and a low-level lifting mechanism. However, a sounding analysis showed that a low-level inversion layer and high LFC would prevent convection initiation because the convective updraft velocities required to overcome the convective inhibition (CIN) were much higher than updraft velocities typically observed in convergence zones. Radar refractivity retrievals from the Twin Lakes, Oklahoma (KTLX), Weather Surveillance Radar-1988 Doppler (WSR-88D) showed a moisture pool contributing up to a 28C increase in dewpoint temperature where the initial storm-scale convergence was observed. The analysis of the storm-relative wind field revealed that the developing storm ingested the higher moisture associated with the moisture pool. Sounding analyses showed that the moisture pool reduced or nearly eliminated CIN, lowered the LFC by about 500 m, and increased CAPE by 2.5 times. Thus, these small-scale moisture changes increased the likelihood of convection initiation within the moisture pool by creating a more favorable thermodynamic environment. The results suggest that refractivity data could improve convection initiation forecasts by assessing moisture variability at finer scales than the current observation network.

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On Upper Tropospheric Kinematics and Severe Weather Occurrence

Cited by 38 publications

References 0 publications

The Use of Moisture Flux Convergence in Forecasting Convective Initiation: Historical and Operational Perspectives

The Use of Moisture Flux Convergence in Forecasting Convective Initiation: Historical and Operational Perspectives

Banded Convection Caused by Frontogenesis in a Conditionally, Symmetrically, and Inertially Unstable Environment

A Case Study on the Impact of Moisture Variability on Convection Initiation Using Radar Refractivity Retrievals

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